Mr Ai thanked reporters waiting outside his studio on Wednesday for their support but said under the conditions of his release he was not able to say more.

The Xinhua news agency said the decision to release him was also taken because Mr Ai suffers from a chronic disease, quoting Beijing police. He is known to suffer from diabetes and high blood pressure.

Mr Ai, 53, is an outspoken critic of the Chinese government had not been heard from since he was arrested at Beijing airport on April 3.

The news agency reported: "The decision comes also in consideration of the fact that Ai has repeatedly said he is willing to pay the taxes he evaded, police said."

Authorities claim that: "The Beijing Fake Cultural Development Ltd., a company Ai controlled, was found to have evaded a huge amount of taxes and intentionally destroyed accounting documents, police said."